Radiation Safety Issues for Radiologic Technologists

Transcription

1 Radiation Safety Issues for Radiologic Technologists Greg Sackett, M.S., CHP Medical Physicist Radiation Worker Risks? 1

2 Patient Risks? Acute Effects? Delayed Effects? Patient Questions? Radiation Dose Limits Dose limits are used to provide a basis for radiation worker safety Whole body limits are designed to reduce stochastic risk (i.e. cancer) to less than 1 in 10,000/yr (10-4 yr -1 ) Risk Equivalent to Safe Occupations Additional limits are designed to reduce deterministic effects (i.e. cataracts) 2

3 NCRP Dose Limits Category mrem/yr Effective dose (whole body) 5000 Lifetime Effective dose 1000 x age Lens of eye 15,000 Organs, skin, extremities 50,000 Public (frequent exposure) 2% of rad worker (100 mrem) Public (infrequent exposure) 10% of rad worker (500 mrem) Embryo/Fetus Total 500 Embryo/Fetus monthly 50 Regulatory Dose Limits Body Part NRC/KS Limit (mrem/yr) MO Limit (mrem/yr) Whole Body Lens of Eye Extremities Pregnant Worker Public

4 Typical Occupational Exposures Category Avg. Annual Dose (mrem) Uranium miners 1200 Nuclear power operations 600 Airline crews 170 Rad and NM Techs 100 Radiologists (Non- Interventionalist) 70 Scatter - The Source of Operator Exposure Staff do not receive exposure from the primary x-ray beam Exposure comes from scattered radiation as soon as the beam strikes an object (usually the patient or table) Larger patients = more scatter Higher kvp/mas = more scatter Larger field of view = more scatter 4

5 Cardinal Principles of Radiation Protection * Time Distance Shielding * External Exposure Hazards Only Time The amount of exposure an individual receives is directly proportional to the time of exposure. Therefore, minimize the amount of time spent with a radiation source. Exposure = Exposure Rate x Time 5

6 Time Time of fluoro procedures should be kept to a minimum Fluoro should alternate on-off, rather than constant on Pulsed Progressive fluoro can reduce patient and caregiver dose by 90% or more Fluoroscopes have 5 minute reset timers to remind users of time elapsed Distance (Doubling the distance from the source will decrease the exposure by four) 6

7 Distance X-ray, CT, LINAC staff should be outside the room (or behind shielding) when machine is on Fluoro remain as far away from patient as possible when fluoro is on Just two steps back can greatly reduce exposure Immobilization If a patient moves during an exposure, the image will be blurred Repeat exam often necessary, resulting in increased patient dose Tech must have patient cooperation or immobilize area Variety of restraining devices can be used 7

8 Patient Holding Mechanical devices should be used If mechanical device impractical, then relative or friend of patient should hold Non-radiology workers could be used as last resort Protective apparel should always be worn by holder In some states, techs holding patients is illegal or log books are required Shielding Any object between you and a source of radiation will provide some shielding. In general, the more dense an object or material, the better the shield. 8

9 Protective Apparel Must be worn during fluoro and possibly mobile imaging Lead aprons do not stop 100% of x- rays Recommended to contain at least 0.5mm lead equivalent CV and Interventionals should use wrap-around aprons Aprons must be inspected annually for leaks and stored appropriately Correction factors may be applied for personnel dose calculations Apron Effectiveness 9

10 Additional Shielding Drapes and equipment aprons Ceiling mounted face shields (can reduce exposure by up to 40 times!) Mobile shields for stationary staff like anesthesia techs (can virtually eliminate exposure) Radiation Safety by Modality Fluoroscopy Interventional Mammography CT Surgery Mobile 10

11 Fluoroscopy Personnel exposure directly related to beam on time Tube should be below patient Techs should use ALARA principles to reduce dose Time Distance Shielding Interventional Radiology and Cardiology Exposures higher due to longer beam on time for procedures and cineradiography Extremity exposures often significant 11

12 Risk to Patients Patient Skin Effects Effect Transient Erythema Threshold (rad) Fluoro On-time (hr) Cine On-time (hr) Delay Hours Epilation weeks Erythema days Moist Desquamation Dermal Necrosis Secondary Ulceration weeks > 10 weeks > 6 weeks 12

13 Typical Patient Dose TIPS Nephrostomy Procedure Neuroembolization Head Neuroembolization Spine IVC Filter Placement Biliary Drainage Hepatic Embolization Percutaneous Coronary Intervention PTCA & CA Patient Dose 217 rad 25.8 rad 198 rad 374 rad 19.3 rad 78.1 rad 196 rad 200 rad 141 rad Projections Vertical PA 30 from Vertical 13

14 Projections Horizontal Vertical AP (not recommended) Proximity of C-Arm to Patient Place detector as close to patient as possible Will reduce patient dose and scatter Place tube as far from patient as possible Do not remove spacer cones 14

15 Collimation Collimate tightly to the area of interest. Reduces the patient s total entrance skin exposure. Improves image contrast. Scatter radiation to the operator will also decrease. Collimation Always collimate as much as possible If the video image is circular you aren t collimating 15

16 Mammography Low personnel exposures Normal walls and barriers adequate Dosimetry probably not required Mammography Dose Primary impact on patient dose is number of views (ESE~800 mrem/view) Therefore, for screening, no more than 2 views per breast recommended (4 for implants) Tomosynthesis doses are higher but will likely prevent additional views Thyroid shields are not required 16

17 Computed Tomography Personnel exposures low Collimated beam results in low scatter Personnel can remain in room if necessary with lead aprons CT Patient Doses Only 5% of all exams are CT, yet CT accounts for ~35% of patient dose Approximately 3000 to 5000 mrad for head scan 2000 to 4000 mrad for body imaging Highly collimated beam allows for avoidance of radiosensitive organs Patient shielding not usually necessary 17

18 CT Patient Doses Patient doses can be large (> 6 Gy) Dependent upon protocol techniques (so they should be reviewed) Machine reported CTDI is NOT the actual patient dose CT Patient Doses 18

19 CT Dose Low noise, high resolution images result in high patient dose Goal is to produce best possible image with reasonable dose Key is proper review of protocols Surgery Surgery personnel often concerned about doses Actual doses are generally low and staff are often not provided dosimetry Pain Clinic physicians may be the exception 19

20 Surgery Who runs the equipment? Portable c-arm safety techniques are similar to interventional rooms If image quality acceptable, use low dose settings Mobile Radiography Usually low personnel doses Exposure cord long enough for tech to be out of scatter area Be aware of location of tube/image receptor Beware of other staff/patients/visitors 20

21 Mobile Radiography It is often not practical to stand more than 6 feet away Techs should wear aprons Criteria for where to stand: Must be able to quickly access patient Must be able to communicate with patient Must be able to communicate with x-ray operator Occupational Radiation Monitoring Required if worker expected to exceed 10% of annual limits (500 mrem) Some states require all machine users to wear dosimeters Dosimeters offer no protection, just record exposure 21

22 Dosimeter Location During fluoro procedures, dosimeter should be worn on the collar outside the lead apron For non-fluoro users, the NCRP recommends wearing the badge at the waist or chest Fetal badges should be worn at the waist, under a lead apron Dosimetry Reports Dose data must be maintained indefinitely Reports deep dose, eye dose and shallow (skin) dose Maintains current, quarterly, annual and lifetime doses 22

23 X-Rays and Pregnancy Human body is most sensitive to radiation effects before birth Pregnant Patients? Effects Time Dependent Dose Dependent Pregnant Workers Radiation workers who become pregnant are rarely at any significant risk of exposure Pregnant worker WILL be concerned about her exposure Training should be provided to inform her of potential risks and available options 23

24 Declared Pregnancy Pregnant worker may declare pregnancy to RSO Entitles worker to lower dose limits (500 mrem, 50 mrem/month) Additional monitoring (monthly) Possible change of duties Cannot be forced to declare pregnancy Discussing Risk with Patients Keys: Tell the truth; Use positive or neutral terms and no jargon; Use examples to help the patient understand; Don t speculate, discuss only the procedure being performed; Do not attack the patient s beliefs or a source of misinformation; Ask if you are being understood. 24

25 Discussing Risk with Patients Risk of cancer induction is age dependent Remember to emphasize the BENEFITS of the procedure If you can t answer question, refer to Radiologist or RSO Radiation Safety Officer Many institutions have an RSO Required by Radioactive Materials License Often a Radiologist 25

26 Radiation Safety Officer Duties Ensure workplace safe for patients and staff Ensure compliance with state/federal regulations Provide safety training to staff Counsel patients Maintain records Reducing Occupational Exposure 95% of tech doses come from fluoro and mobile radiography Use Time, Distance and Shielding to keep doses ALARA Pay attention to fluoro times Be aware of direction of primary beam Use provided aprons and shields 26

27 Reducing Unnecessary Patient Dose Unnecessary examinations Radiologist controlled Repeat Examinations Tech controlled Radiographic Technique High kvp/low mas reduces patient dose May result in lower contrast issphysics.com QUESTIONS? 27